diff --git a/src/avlTree.js b/src/avlTree.js
index 1228ba5..30fc56c 100644
--- a/src/avlTree.js
+++ b/src/avlTree.js
@@ -7,6 +7,17 @@
 const { BinarySearchTree } = require('./binarySearchTree');
 const { AvlTreeNode } = require('./avlTreeNode');
 
+/**
+   * Get the node's height
+   * @private
+   * @param {AvlTreeNode} node
+   * @return {number}
+   */
+function getNodeHeight(node) {
+  if (!(node instanceof AvlTreeNode)) return 0;
+  return node.getHeight();
+}
+
 /**
  * @class AvlTree
  * @extends BinarySearchTree
@@ -31,13 +42,17 @@ class AvlTree extends BinarySearchTree {
     node.updateHeight();
     const balance = node.getBalance();
     if (balance > 1) {
-      if (node.getLeft().hasLeft()) {
+      const LL = node.getLeft().getLeft();
+      const LR = node.getLeft().getRight();
+      if (getNodeHeight(LL) >= getNodeHeight(LR)) {
         node.rotateRight();
       } else if (node.getLeft().hasRight()) {
         node.rotateLeftRight();
       }
     } else if (balance < -1) {
-      if (node.getRight().hasRight()) {
+      const RR = node.getRight().getRight();
+      const RL = node.getRight().getLeft();
+      if (getNodeHeight(RR) >= getNodeHeight(RL)) {
         node.rotateLeft();
       } else if (node.getRight().hasLeft()) {
         node.rotateRightLeft();
diff --git a/test/avlTree.test.js b/test/avlTree.test.js
index 3b370d1..f0bbe30 100644
--- a/test/avlTree.test.js
+++ b/test/avlTree.test.js
@@ -175,6 +175,82 @@ describe('AvlTree tests', () => {
       expect(root.getLeft().getLeft().getRight().getValue()).to.equal(20);
       expect(root.getLeft().getLeft().getLeft().getValue()).to.equal(10);
     });
+
+    it('keep balance when inserting so many elements', () => {
+      const elements = [
+        130, 345, 826, 571, 795, 366, 648, 418, 353, 267, 450, 404, 456, 310,
+        137, 888, 497, 378, 651, 148, 552, 632, 886, 532, 273, 802, 590, 187,
+        487, 781, 24, 775, 746, 664, 459, 180, 76, 252, 44, 439, 426, 444, 91,
+        817, 152, 5, 643, 381, 470, 864, 307, 83, 753, 792, 216, 650, 780, 863,
+        396, 750, 494, 855, 684, 508, 837, 849, 654, 812, 561, 86, 731, 845,
+        176, 851, 110, 673, 222, 874, 512, 856, 609, 403, 872, 141, 488, 150,
+        70, 357, 705, 260, 805, 233, 172, 890, 519, 230, 824, 335, 447, 563,
+        613, 62, 597, 659, 166, 185, 93, 666, 634, 195, 767, 729, 803, 520, 626,
+        284, 569, 704, 225, 228, 440, 234, 526, 105, 202, 751, 809, 762, 341,
+        631, 857, 169, 43, 115, 147, 513, 773, 299, 674, 865, 259, 493, 629,
+        164, 555, 437, 101, 866, 287, 821, 380, 711, 337, 212, 458, 45, 733,
+        576, 60, 755, 415, 384, 311, 51, 301, 540, 74, 756, 742, 675, 776, 181,
+        862, 847, 490, 516, 423, 760, 114, 876, 306, 405, 116, 385, 541, 624,
+        501, 873, 867, 16, 698, 617, 323, 354, 359, 700, 644, 179, 502, 397,
+        304, 0, 635, 881, 171, 671, 454, 87, 266, 551, 207, 695, 592, 743, 268,
+        198, 72, 550, 283, 758, 292, 189, 340, 194, 278, 507, 689, 145, 472,
+        269, 199, 346, 870, 431, 333, 363, 433, 578, 464, 779, 668, 827, 577,
+        715, 162, 167, 136, 210, 399, 89, 248, 184, 35, 524, 330, 640, 157, 350,
+        182, 622, 846, 586, 99, 549, 358, 58, 410, 4, 686, 139, 28, 258, 491,
+        575, 842, 825, 138, 618, 174, 660, 395, 871, 801, 749, 504, 383, 589,
+        103, 17, 241, 281, 797, 796, 499, 361, 104, 264, 247, 478, 804, 682,
+        294, 481, 732, 126, 683, 800, 669, 356, 81, 432, 71, 701, 288, 777, 221,
+        759, 892, 370, 736, 257, 477, 783, 134, 515, 771, 612, 411, 467, 838,
+        272, 238, 829, 160, 132, 409, 55, 376, 823, 446, 7, 791, 155, 730, 500,
+        788, 317, 460, 108, 430, 680, 453, 547, 442, 158, 316, 250, 601, 390,
+        14, 201, 39, 9, 884, 244, 583, 559, 251, 681, 702, 420, 371, 78, 763,
+        73, 531, 794, 232, 389, 498, 620, 554, 533, 391, 436, 754, 355, 882,
+        744, 522, 836, 196, 806, 125, 293, 107, 455, 297, 120, 891, 18, 435,
+        652, 206, 122, 853, 203, 564, 394, 412, 320, 56, 766, 832, 633, 6, 835,
+        124, 153, 312, 748, 47, 840, 82, 364, 839, 761, 97, 672, 457, 786, 553,
+        61, 170, 22, 703, 351, 112, 95, 517, 200, 774, 485, 121, 163, 204, 523,
+        25, 720, 558, 348, 466, 41, 29, 237, 177, 119, 741, 253, 336, 37, 331,
+        401, 42, 173, 614, 19, 608, 770, 858, 143, 217, 52, 570, 117, 128, 276,
+        539, 113, 308, 785, 496, 298, 852, 480, 670, 518, 2, 419, 159, 118, 814,
+        724, 588, 461, 714, 226, 628, 286, 186, 468, 98, 208, 712, 630, 627,
+        861, 213, 413, 734, 448, 400, 798, 271, 373, 854, 495, 573, 765, 96,
+        382, 707, 893, 285, 710, 313, 525, 154, 621, 521, 725, 591, 641, 300,
+        696, 790, 645, 146, 535, 282, 565, 691, 572, 639, 12, 657, 256, 23, 85,
+        690, 38, 3, 584, 64, 605, 543, 144, 607, 449, 649, 360, 557, 492, 372,
+        548, 161, 342, 615, 407, 223, 625, 850, 655, 568, 10, 205, 427, 386,
+        820, 197, 123, 249, 131, 735, 667, 129, 319, 100, 465, 567, 616, 191,
+        277, 619, 48, 594, 723, 819, 462, 242, 245, 463, 193, 79, 843, 647, 231,
+        566, 606, 402, 739, 322, 810, 542, 328, 127, 813, 40, 209, 537, 329,
+        510, 476, 102, 860, 374, 602, 429, 69, 220, 676, 599, 527, 424, 362,
+        534, 822, 11, 658, 663, 818, 236, 54, 63, 808, 637, 109, 393, 406, 57,
+        32, 142, 556, 708, 506, 772, 869, 67, 688, 596, 31, 885, 1, 365, 219,
+        503, 709, 344, 326, 367, 332, 229, 263, 600, 706, 560, 604, 175, 868,
+        408, 452, 26, 587, 377, 243, 697, 279, 740, 505, 638, 595, 581, 718, 21,
+        324, 347, 227, 562, 421, 218, 646, 752, 59, 156, 489, 84, 302, 88, 699,
+        50, 135, 653, 875, 388, 685, 434, 77, 745, 445, 878, 290, 677, 255, 275,
+        484, 178, 880, 585, 192, 149, 387, 441, 90, 679, 289, 545, 66, 49, 694,
+        623, 536, 769, 469, 111, 728, 443, 33, 240, 580, 375, 80, 486, 471, 687,
+        859, 830, 94, 530, 879, 270, 30, 833, 816, 722, 579, 352, 574, 528, 887,
+        509, 831, 318, 417, 327, 727, 261, 665, 799, 325, 719, 598, 214, 544,
+        188, 811, 254, 190, 721, 379, 656, 782, 13, 274, 793, 309, 482, 392,
+        889, 768, 338, 713, 841, 451, 661, 717, 349, 848, 538, 726, 133, 483,
+        807, 343, 747, 883, 165, 738, 593, 92, 369, 877, 315, 787, 716, 321,
+        339, 235, 778, 438, 20, 27, 183, 34, 844, 757, 737, 636, 834, 479, 692,
+        603, 303, 678, 828, 239, 789, 46, 425, 414, 474, 246, 514, 815, 662,
+        546, 582, 610, 140, 151, 473, 168, 65, 75, 475, 211, 224, 529, 368, 36,
+        280, 215, 262, 334, 511, 296, 8, 53, 15, 693, 295, 68, 428, 784, 398,
+        106, 291, 764, 305, 422, 416, 611, 314, 642, 265
+      ];
+
+      const tree = new AvlTree();
+      elements.forEach((n) => tree.insert(n));
+      tree.traversePreOrder((node) => {
+        const balance = node.getBalance();
+        if (balance > 1 || balance < -1) {
+          throw new Error(`not balance , balance is ${balance}`);
+        }
+      });
+    });
   });
 
   describe('.min()', () => {